This is a proposal for the development of inorganic models for water oxidation and dinitrogen reduction. Although seemingly unrelated, in some ways these reactions are the microscopic reverse of each other, and models for both exist in polypyridyl complexes of Ru and Os. The mechanism of water oxidation by the blue dimer [(bpy)2(H2O)RuIIIORuIII(H2O)(bpy)2}4+ (bpy is 2,2'-bipyridine) will be pursued by a combination of kinetic, spectroscopic, and 18O labeling studies. The goal is to establish pathways and analogies that may be of relevance to photosystem II. The role of chloride catalysis, in this case by a chemical mechanism involving HOC1, will be investigated and new models for water oxidation developed. In light of the recent structural determination of a nitrogenase enzyme, a role must be found for binding and reduction of N2 by Fe. Viable models for such pathways will be pursued based on polypyridyl complexes of Os and earlier mechanistic proposals by Chatt et al. and Schrock et al. They are based on a new series of hydrazidos complexes of OsIV, [OsIV(tpy)(NNR2)]2+ (tpy is 2,2':6',2"-terpyridine, -NR2 is NEt2 or morpholine). Oxidation of these complexes to OsVI hydrazidos and reduction to free amine, HNR2, and [OsII(tpy)(NH3)]2+ via intermediate hydrazines will be investigated as models for the key redox steps in N2 reduction, as will the role of imido and diazenido intermediates. The hydrazido reactivity will be extended to a more electron-rich coordination environment by N-N coupling based on [Os(tpy)(C12(N)]+. Dinitrogen complexes will be prepared and their reactivity with acid to give OsVI hydrazidos explored.